http://celestialdelights.info/pub/SN1006_1.htm

Nearly one millennium ago, the sudden appearance of the brightest star in
recorded history puzzled and frightened sky watchers around the world. The
new star of 1006 was actually a nearby supernova, the visible manifestation
of a star's complete destruction. At peak brightness it outshone Venus and
was even compared with the moon. Just how bright it was, though, has been
something of a mystery estimates in the scientific literature have ranged
over a factor of fifteen. Recently, a team led by Frank Winkler of Vermont's
Middlebury College reported that it has found the answer in faint strands of
gas at the site of the explosion.